Finite-element analysis of severe plastic deformation in differential-speed rolling

Abstract

Differential-speed rolling can impose severe plastic deformation on a metallic sheet by developing extensive shear strain. Plastic deformation by a single pass with a speed ratio of 3 was found to be as high as 3.5 in terms of the effective strain. Although the speed ratio, the friction coefficient and the length of deformation zone are important parameters in controlling the differential-speed rolling, their effects on plastic deformation are yet unknown. In the present study, these effects were investigated by the rigid-plastic finite-element analysis, and as a result logics in dissipation of power, mechanisms in development of plastic deformation and an upper limit of the speed ratio were found. Moreover, a double-pass differential-speed rolling was introduced to achieve a symmetric distribution of the effective strain through thickness of a sheet. An excessive speed ratio would waste unnecessarily a portion of the power through friction at the interface between the sheet and rolls, and also exert a tensile stress in the sheet, which could result in fracture if the material of the sheet is as brittle as a magnesium alloy.